Spark plug



Nov. 10, 1953 L. M9K. FIELD 2,658,934

SPARK PLUG Filed May 25, 1951 INVENTOR ATTORNEY Patented Nov. 10, 1953 UNITED STATES PATENT OFFICE SPARK PLUG Application May 25, 1951, Serial No. 228,282

4 Claims.

This invention relates to an improved spark plug of the general type in which a valve-controlled passage admits a fluid to the engine cylinder equipped with said plug, upon each intake stroke of the piston.

The plug includes an insulator which for manufacturing advantage is transversely divided into upper and lower abutting sections, said insulator sections having central fluid admission ports. At least one of the insulator sections is formed with a recess communicating with the upper and lower ports and receiving the valve. This valve is in the form of a head on the upper end of a lower central positive electrode section which is reciprocable in the lower port and is coop-erable with a negative electrode carried by a metal shell in which the insulator is secured.

When a plug of this type i used in a presentday high-compression engine, the high compression within the cylinder greatly resists the jumping of the spark across the spark gap. Thus, if there be any reduced pressure zone at the inner side of the shell into which any compressed gas may flow between the abutting insulator sections, the resistance to jumping of the high tension current to said shell will be less along such a path of gas flow than across the spark gap, with the result that the plug will short and fail to fire. The use of a sectional insulator in a plug of the type under consideration, therefore,

presents the problem of effectively preventing any compressed gas travel from the valve-containing chamber to the shell between the insulator sections.

It is the principal object of the present invention to solve the above problem in a simple yet effective way, by providing an improved construction in which the zone of contact of the abutting insulator sections, is subjected at both its inner and outer peripheries to the compression within the cylinder. By thus equalizing the pressure at the inner and outer peripheries of the zone of contact of the insulator sections and the pressure to which the spark gap is subjected, there will be no compressed gas flow between the insulator sections, no reduced pressure zone at the inner side of the shell, and no path of possible current travel having less resistance than the spark gap, with the result that the plug will effectively fire.

In carrying out the above end, a further object is to make extremely simple provision whereby the compressed gas in the cylinder may reach both the inner and outer peripheries of the zone of contact of the insulator sections.

Another object of the invention is to provide a novel construction in which it is only necessary to provide a compression seal between the upper insulator section and the metal shell.

A still further object is to make novel provision for conducting the high tension current from the upper to the lower section of the central positive electrode.

Yet another object is to provide a novel construction which may be expeditiously manufactured and profitably marketed at a reasonable price.

With the above and other objects in view that will become apparent as the nature of the invention is better understood, the same consists in the novel form, combination and arrangement of parts hereinafter more fully described, shown in the accompanying drawing, and claimed.

In the drawing:

Figure 1 is a longitudinal sectional view of a spark plug embodying the improvements,

Figure 2 is a lower end view of the upper insulator section, and

Figure 3 is an upper end view of the lower insulator section.

In the drawing, a construction has been shown which is well adapted to the attainment of the desired ends, and while this construction will be rather specifically described, it is to be understood that variations may be made within the scope of the invention.

A metal shell 5 is provided having a threaded lower end 6 for reception in the usual spark plug opening of an internal combustion engine cylinder head. The side wall I of the shell 5 has a relatively large internal diameter 8 at its upper end, a small diameter 9 between its ends, and a still smaller diameter It at its lower end. This construction provides an upper inverted frustoconical bore H and a lower inverted frustoconical bore I 2 in the shell. The upper end of the shell carries an insulator-clamping ring nut 13 and the lower end of said shell is provided with a suitable negative electrode M.

The insulator comprises an elongated upper section [5 and a relatively short lower section [6. The upper section [5 is provided with an inverted frusto-conical lower end I! seated upon the air seal l8 engaging the upper bore II and is held tightly in place by the rin nut IS. The lower section It is formed with an inverted frusto-conical portion forming a shoulder l9 engaging the bore 1 2 but no attempt is made to provide a gas-tight engagement of said shoulder l9 with said bore l2. In fact, flow of gas is purposely allowed between the contacting surfaces of said insulator section It and said bore. A gas passage to permit this flow between the shoulder l9 and bore l2, may be provided by allowing tolerances in manufacture, to give a not-too-accurate fit between said shoulder and bore, or other provision could well be made for attaining the desired end. The presence of a sufiiciently imperfect fit to provide the gas passage is represented in the drawing by the heavy lines 20.

Above the bore 12, the insulator section it has clearance 2| with the diameter 53 of the shell wall I, and the upper end of said section It may be reduced at its outer periphery to provide a distinct circular chamber 22. Compressed gas from the engine cylinder reaches this chamber 22 through the passages 28 and 2! upon each compression stroke of the piston, for a purpose to appear.

The insulator sections l5 and 16 have abutting inner ends 24 and 25 respectively, and no attempt to have these inner abutting ends fit each other in a gas-tight manner is necessary. The upper insulator section I5 is formed with a central fluid port 26 from end to end. The lower section 16 is provided with a recess 21 in its upper end, and also has a port 28 from said recess 21 to its lower end. The bottom of this recess 21 is rormea with grooves 29 radiating from the port A lower, reciprocable, central, positive electrode section 30 is loosely received in the port 28, the

lower end of said electrode section 30 being laterally spaced from the inner end of the negative electrode 14. The upper end of the electrode sectionto is provided with a suitable valve head 3| loosely received in the recess 27, to engage the seat 32 which is a part of the insulator section 15, upon each compression stroke of the piston. Upon each intake stroke, the electrode section 30 and the valve head ,3l lower, thereby admitting fluid through the port 26, recess 21,

and port 28. The grooves 29 prevent the valve fluid enters the cylinder through the tubular upper electrode section 33, port 26, recess 21, grooves 29 and port 28. Upon each compression stroke the valve head 3| is forced upwardly and seats against the seat 32, preventing loss of com pression. Also, during each compression stroke,

compressed gas enters the recess 21 through the port 28 and enters the chamber through the passages 20 and 21. Thus, the pressure at the inner and outer peripheries of the contacting surfaces 24 and 25 of the insulator sections and the pressure to which the spark gap is subjected,

is equalized. The result is that the high tension current cannot jump from the central electrode to the shell wall 1 with less resistance than it can jump the spark gap. Consequently, the plug will effectively fire regardless of the fact that no seal is provided between the surfaces 224 and -2 5.

While there is herein shown and described the preferred embodiment of the invention, it is nevertheless to be understood that minor changes may be made therein without departing from the spirit and scope of the invention as claimed.

I claim:

l. A spark plug comprising a shell having grounding means, an insulator divided into an upper section and a lower section, said insulator sections having abutting ends within said shell,

the inner end of at least one of said insulator sections having an internal recess, said upper insulator section having a'fluid port "extending 4 to said recess, said lower insulator section having a central port extending from said recess to the lower end of said lower section, the inner periphery of the zone of contact of said abutting insulator sections being subjected to gas pressure entering said recess through said lower port during engine operation, gas-conducting means extending to the outer periphery of said zone of contact and open toward the lower end of the plug for subjecting said outer periphery to the same gas pressure as said inner periphery, means fixedly mounting said insulator sections in said shell, said mounting means including inclined contacting surfaces between said upper insulator section and said shell, said contacting surfaces being above the aforesaid zone of contact between the insulator sections, a central positive electrode section loosely reciprocabl'e in said lower port and having a valve head in the aforesaid recess to close said upper port when raised, and means for conducting current to said central electrode section.

'2. A structure as specified in claim 1-; said mountin means for said insulator sections including an upwardly facing inverted frusto-conical bore in said shell and an inverted frustoconical shoulder on said lower insulator section, said shoulder and bore having such engagement as to provide a gas passage between them, said gas passage forming a portion of said gas-{conducting means, said lower insulator section having clearance with said shell from said gas passage to the upper endof said lower insulator section, said clearance forming another portion of said gas-conducting means.

3. A structure as specified in claim 1; said mounting means for said insulator sections including an upwardly facing inverted frusto-conical bore in said shell and an inverted fr'ustoconical shoulder on said lower insulator section, said shoulder and bore having such engagement as to provide a gas passage between them, said gas passage forming a portion of said gas-conducting means, said lower insulator'secti-on having clearance with said shell from said gas passage to the upper end of said lower insulator section, said clearance forming another portion of said gas-conducting means, said upper'end of said lower insulator section having are'duced diameter providing a circular chamber around the aforesaid 'zone of contact, said chamber bompleting said gas-conducting means.

4. A structure as specified in claim 1,"th e inner end of one of said insulator sections being of reduced diameter to provide a circular chamber around said outer periphery of said zone 'of contact, saidchamber forming a. portion of said gas-conducting means, the upper extremity of said lower insulator section being or reduced diameter 'to provide a circular chamber around said outer periphery of said zone of contact, said chamber forming a portion of'sa id "g'as conductmg means.

LLOYD MCKINSEY FIELD.

References Cited in the file of thispatent UNITED STATES PATENTS Number Name Date 1,430,964 Faber l Oct. 3, 1922 1,534,065 Korcz'ynski Apr. 21, 1925 1,985,192 OMarra Dec. 18, I934: 2,142,383 Smith Jan. 3,1939 

